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Nonlocal Dual-Band Reconfigurable Intelligent Surfaces for Precise Full-Space Beamforming

Moosung Kim, Minseok Kim

TL;DR

This work tackles the challenge of precise full-space beamforming with RIS in dual bands by introducing a nonlocal, dual-band RIS whose interleaved sub-cells decouple the two frequencies. An MNT-based synthesis framework models the RIS as a multiport network and optimizes diode loads to independently shape far-field patterns at $f_1=4.0$ GHz and $f_2=6.3$ GHz. A $14\times14$ varactor-based prototype demonstrates single-beam, dual-beam, and sector-pattern synthesis in full space, with experimental results matching simulations and confirming band decoupling. The approach enables versatile, high-fidelity dual-band beamforming suitable for multifunctional wireless systems, including ISAC-like scenarios, at the two target frequencies $f_1$ and $f_2$.

Abstract

This paper introduces a nonlocal, dual-band reconfigurable intelligent surface (RIS) designed for full-space beam synthesis at 4.0 GHz and 6.3 GHz. The constituent unit cells comprise a pair of interleaved sub-cells that are specifically engineered to operate independently at their respective target frequencies. This hardware-level decoupling facilitates an efficient synthesis framework based on microwave network theory (MNT) that rigorously accounts for mutual coupling within both bands. Under this framework, the optimal biasing for sub-cells is determined to achieve precise full-space beam synthesis at both frequencies. The proposed method is numerically and experimentally validated with an RIS comprising 14 X 14 varactor-loaded unit cells that can be individually biased. We experimentally demonstrate arbitrary beam profile synthesis beyond simple beam steering, including dual-beam and sector patterns in full space. Experimental and simulation results show good agreement with the MNT model, confirming the effectiveness of the proposed method.

Nonlocal Dual-Band Reconfigurable Intelligent Surfaces for Precise Full-Space Beamforming

TL;DR

This work tackles the challenge of precise full-space beamforming with RIS in dual bands by introducing a nonlocal, dual-band RIS whose interleaved sub-cells decouple the two frequencies. An MNT-based synthesis framework models the RIS as a multiport network and optimizes diode loads to independently shape far-field patterns at GHz and GHz. A varactor-based prototype demonstrates single-beam, dual-beam, and sector-pattern synthesis in full space, with experimental results matching simulations and confirming band decoupling. The approach enables versatile, high-fidelity dual-band beamforming suitable for multifunctional wireless systems, including ISAC-like scenarios, at the two target frequencies and .

Abstract

This paper introduces a nonlocal, dual-band reconfigurable intelligent surface (RIS) designed for full-space beam synthesis at 4.0 GHz and 6.3 GHz. The constituent unit cells comprise a pair of interleaved sub-cells that are specifically engineered to operate independently at their respective target frequencies. This hardware-level decoupling facilitates an efficient synthesis framework based on microwave network theory (MNT) that rigorously accounts for mutual coupling within both bands. Under this framework, the optimal biasing for sub-cells is determined to achieve precise full-space beam synthesis at both frequencies. The proposed method is numerically and experimentally validated with an RIS comprising 14 X 14 varactor-loaded unit cells that can be individually biased. We experimentally demonstrate arbitrary beam profile synthesis beyond simple beam steering, including dual-beam and sector patterns in full space. Experimental and simulation results show good agreement with the MNT model, confirming the effectiveness of the proposed method.
Paper Structure (6 sections, 5 equations, 5 figures)

This paper contains 6 sections, 5 equations, 5 figures.

Table of Contents

  1. Introduction
  2. Proposed Unit-Cell Architecture
  3. MNT-Based Nonlocal Design Framework
  4. Optimization of Varactor Capacitance
  5. Full-wave and Experimental Verifications
  6. Conclusion

Figures (5)

  • Figure 1: The proposed band-decoupled dual-band reconfigurable intelligent surface. The unit cell’s dimensions are shown in millimeters (mm).
  • Figure 2: The reflection coefficient of the unit cell at (a) $f_1$ and (b) at $f_2$ under periodic boundary conditions, illustrating that the modulation of sub-cells at $f_1$ (or $f_2$) is transparent at $f_2$ (or $f_1$).
  • Figure 3: Near-field measurement setup of the dual-band RIS: feed horn and a $14\times14$ RIS panel composed of two $14\times7$ modules.
  • Figure 4: UV-plane radiation patterns for the synthesized dual-band RIS: (a),(b) unidirectional beam steering at $f_1$ and $f_2$, respectively; (c),(d) dual-beam synthesis at $f_1$ and $f_2$, respectively; and (e),(f) sector-pattern synthesis at $f_1$ and $f_2$, respectively.
  • Figure 5: Measured $u$--$v$ directivity maps demonstrating the band-decoupled characteristics of the dual-band RIS.